The quadrifilar helix antenna (QHA) has been widely advocated for use, inter alia, in mobile satellite communications systems. Compared with crossed dipole and patch antennas, the QHA offers the advantages that it has a small, compact structure, is relatively insensitive to the effects of handling and of the ground and has a radiation pattern and a wide circularly polarised beam that can be readily shaped. The so-called printed QHA (PQHA) is particularly advantageous because of its light weight, low cost, high dimensional stability and ease of fabrication.
Although existing PQHA structures are already quite small, further size reduction is still required to satisfy the space limitations in handheld mobile communications terminals.
Various approaches have been adopted with a view to reducing the physical size of a QHA. One approach involves loading the QHA with a dielectric material such as Zirconium Titinate ceramic. Although this gives significant size reduction, the operating bandwidth of the antenna is very small, typically about 30 MHz which is unsatisfactory for many mobile communications applications.
A coupled-segment QHA has also been proposed. In this case the helical antenna filaments are separated into upper and lower segments which are interleaved in overlapping fashion. This approach only provides a small percentage of size reduction.